From mboxrd@z Thu Jan  1 00:00:00 1970
From: greg@kroah.com (Greg KH)
Date: Thu, 14 Aug 2014 05:40:54 +0800
Subject: Strategies for accessing driver data from file operations!?
In-Reply-To: <53EB5E3B.20508@gmail.com>
References: <53EA1AE8.1030509@gmail.com> <20140812195328.GA20273@kroah.com>
	<53EB5E3B.20508@gmail.com>
Message-ID: <20140813214054.GA7214@kroah.com>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

On Wed, Aug 13, 2014 at 09:46:51AM -0300, Daniel Hilst Selli wrote:
> One last question, supposing I need to create multiple /dev nodes, do I need to
> allocate one struct cdev for each major:minor pair (cdev_alloc(), cdev_init(), cdev_add())?

No, you can allocate multiple minor numbers with a single set of cdev
calls.  But watch out, you also need to create a 'struct device' for
_each_ minor number you are actually using if you want the device nodes
to show up in /dev automatically.

Yeah, it's a pain, sorry, but this way you can allocate a whole range of
major:minor pairs but don't actually expose them to userspace until you
really need them (i.e. the hardware is present in the system.)  This
keeps /dev looking like only the devices that are present in the system,
not the "old" way of "every possible device that could ever be possibly
present".

Hope this helps,

greg k-h